15 February 2014

The human legacy—one of the world's six greatest catastrophes

I was watching with interest the other night Jon Stewart's interview of Elizabeth Kolbert, author of a new book, The Sixth Great Extinction.

There have been five great extinction events in the past 550-million years of multi-celled life on Earth, events in which abnormally large numbers of species die out simultaneously or within a limited time frame. The last, and best known, was the Cretaceous-Tertiary event which wiped out the dinosaurs, caused by a massive comet or meteor striking the Earth 65
million years ago. The cause of some of the others is debated, but we know the cause of the sixth—us. Human activity is having a catastrophic effect on our fellow species.

Stewart's interview had me pondering legacies, not mine I hasten to say, but our species'. Over the great span of geologic time, Homo sapiens will leave a legacy, and what a tragic legacy it is shaping up to be. We are becoming the cause of one of the six greatest die-offs of life on Earth in over half a billion years—a destroyer of worlds.

Yet we are a moral creature and a reasonably intelligent one. One might think such a creature would pause in its activity, and reflect on what it will leave for posterity—its own posterity and the posterity of its home, the planet Earth. But there is little evidence of such reflection. Our leaders are obsessed with growth, of wringing ever more out of the planet and despoiling it in the process.

I have always been an optimist, but I see little room for optimism as I observe the destroyer of worlds march down its awful road. If we don't pause in our obsessions, reflect on our wayward ways, and apply our innate morality to our ambitions, our legacy will be dark indeed.

1 comment:

  1. Bill, you might take a look at paleontologist Peter Ward's "Under a Green Sky" in which he discusses his research into the first four major extinctions. He contends they all arose from rapid warming and acidification of the oceans:

    "First, the world warms over short intervals of time because of a sudden increase of carbon dioxide and methane... The warmer world affects the ocean circulation systems and disrupts the position of the conveyer currents. Bottom waters begin to have warm, low-oxygen water dumped into them. Warming continues, and the decrease of equator-to-pole temperature differences reduces ocean winds and surface currents to a near standstill. Mixing of oxygenated surface waters with the deeper, and volumetrically increasing, low-oxygen bottom waters decreases, causing ever-shallower water to change from oxygenated to anoxic. Finally, the bottom water is at depths were light can penetrate, the combination of low oxygen and light allows green sulfur bacteria to expand in numbers and fill the low-oxygen shallows. They live amid other bacteria that produce toxic amounts of hydrogen sulfide, and the flux of this gas into the atmosphere is as much as 2,000 times what it is today. The gas rises into the high atmosphere, where it breaks down the ozone layer, and the subsequent increase in ultraviolet radi8ation from the sun kills much of the photosynthetic green plant phytoplankton. On its way up into the sky, the hydrogen sulfide also kills some plant and animal life, and the combination of high heat and hydrogen sulfide creates a mass extinction on land. These are the greenhouse extinctions."